Technical Field
The present invention relates to processes and catalysts for production of light olefins. More specifically, the present invention relates to modified silicalite-1 catalysts that may be used to convert 1-butene into ethylene and propylene.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Several on-purpose propylene production technologies are being investigated and have some been commercialized, such as methanol-to-olefins (MTO), propane dehydrogenation, catalytic cracking of butenes and olefin metathesis. Among these methods, butene cracking has attracted much attention due to the availability of large and stable supplies of butenes from FCC and stream cracking processes. The process offers refiners and petrochemical producers a high degree of flexibility to their cracking units. Cracking of butenes appears to be a promising technology for production of ethylene and propylene. There is ongoing research on highly reactive yet selective catalysts for the purpose of light olefin production by cracking of butenes. Currently, the catalysts that are being investigated include H-ZSM-5, H-ZSM-48, MCM-22 and PITQ-13. However, most of these catalysts are acidic in nature and favor the production of higher hydrocarbons, especially C6+ aromatics.
Zhu et al. (Applied Catalysis A: General, 2005, v. 288, pp. 134-142—incorporated herein by reference in its entirety) investigated the effects of zeolite pore structure and Si/Al ratio catalytic cracking of 1-butene to propylene and ethylene over medium-pore 10-membered ring zeolites and the small-pore SAPO zeolite. The smaller the pore size of the zeolites, the greater the extent of suppression of the hydrogen transfer reaction of alkenes, and the higher the propylene selectivity.
Lin et al. (Journal of Catalysis, 2014, v. 309, pp. 136-145—incorporated herein by reference in its entirety) reported that the H-ZSM-5 modified with phosphorous to reduce the number of the strong acid sites showed the best performance in catalytic cracking of 1-butene to propylene. It was suggested that adjusting the acid site distribution is important.
Johnson et al. (U.S. Pat. No. 6,222,087—incorporated herein by reference in its entirety) discloses a catalytic cracking process for producing light olefins rich in propylene from C4-C7 olefins using a catalyst containing ZSM-5 and/or ZSM-11 having initial Si/Al ratio greater than about 300 in a fluidized-bed reactor or a fixed-bed swing reactor.
Voskoboynikov et al. (U.S. Pat. No. 7,314,963—incorporated herein by reference in its entirety) discloses a process for producing propylene and ethylene from catalytic cracking of C4-C10, olefins over a spherical catalyst comprising MFI-type zeolite having Si/Al ratio between 400 and 500 at 500-600° C.
Dath et al. (U.S. Pat. Nos. 6,951,968 and 7,384,883—each incorporated herein by reference in its entirety) describes a method for producing a catalyst for olefin cracking comprising the steps of heating a ZSM-5 catalyst in steam to remove aluminum from the crystalline silicate framework, extracting aluminum from the pores of the catalyst framework by contacting the catalyst with a complexing agent for aluminum to increase the silicon/aluminum atomic ratio of the catalyst and calcining the catalyst at an elevated temperature.
Colombo et al. (European Patent No. EP0109060A1—incorporated herein by reference in its entirety) discloses a process for the conversion of C4-C12 olefins into propylene over zeolites selected from silicalites, boralites, chromosilicates, ZSM-5 and ZSM-11 (Si/Al molar ratio is above 350), at a space velocity of from 5 to 200 kg/h of olefins per kg zeolite and at a temperature of from 400 to 600° C. The silicalite-1 is either ion-exchanged, impregnated, or co-precipitated with a modifying element such as Cr, Mg, Ca, Sr, and Ba.
Heng et al. (Japanese Patent No. JP04335144B2—incorporated herein by reference in its entirety) discloses a process for producing lower olefins (propylene and ethylene) using an MFI zeolite catalyst having Si/Al molar ratio of 280-5000. The variation of C4 olefins in the feed stream (from 0 to 61.2%) was studied and a propylene yield of 32 wt. % was observed at 550° C. using Si/Al molar ratio of 500 and 40 wt. % butenes in a paraffinic feed stream.
In view of the foregoing, the objective of the present invention is to provide new methods and new catalysts for producing ethylene and propylene from butene. The catalysts may be subject to pre-treatment to significantly enhance their production and selectivity toward the light olefins.